yeah, I can't find a stamp on any of the boards or on any of the other 2x10's in the house attic... only have info on the OSB flooring....

but for sag there is virtually no sag when no weight is on it, I think those 1x4's are holding the sag out that go vertical from the ceiling joist to the rafters.... and when stepping on it there is only about an inch of sag in the dead center of the floor...

when stepping on it there is only about an inch of sag in the dead center of the floor...

Using
Beam Supported at Both Ends, Load at Center
fromhttp://www.engineeringtoolbox.com/be...on-d_1312.html
and knowing your weight, you can get close to an E value for your joists, and then work backwards to figure PSF loading.
The problem in this case is that some of your weight is carried by nearby joists so the sag is less than it would be for a single joist on edge.